: The purpose of this work was to clarify the components of the optical origin of the arterial light reflex seen by clinical instruments in normotensive subjects using the direct ophthalmoscope or fundus photography.

Methods

The reflex observed on retinal arterioles with the adaptive optics scanning laser ophthalmoscopes’ (AOSLO) vertical scan stabilized across each arteriole was analyzed. This reflex, produced by a scan across the diameter of the artery at 16 kHz, showed distinct components of different natures. These components were measured relative to the diameter of the vessel and the thickness of the vessels’ wall in each location. These latter measurements were obtained in the indirect mode of the Indiana AOSLO. The arteriolar light reflex width on the en face image of the Heidelberg Spectralis was also measured at the same locations.

Results

A continuous bright narrow band of approximately 7.5 % of the arteriole lumen width as measured by indirect AOSLO imaging, was seen that was stable in images. There was a broader band of narrow lines corresponding to the reflections from individual moving erythrocytes on both sides of the central bright line. This broader band varied in width with the pulse as seen in the changing erythrocyte velocity profile. The maximum breadth of this erythrocyte reflex corresponded in time to the maximal blood flow velocity. This broader band produced by the reflections from erythrocytes in the blood column was comparable to the reflex widths seen with the Heidelberg Spectralis or the Topcon fundus camera. An additional component of the arterial light reflex comes from a temporally stable, spatially irregular reflection from the arteriole wall.

Conclusions

The normal clinically observed arterial light reflex is a reflex with 3 components, a central brightest portion comes from the smooth intra-arteriolar cell free plasma column, another spatially variable component is attributed to structural irregularities of the arteriole wall, and a third dynamic reflex, often accounting for the majority of the clinically observed light reflex width, is dynamic in nature and is added by the optically rough erythrocyte cell column within the arteriole.